Exhaust gas treatment device and nozzle for the same

ABSTRACT

A nozzle ( 1 ) includes a nozzle body ( 10 ), a piston ( 2 ) movably disposed inside the nozzle body ( 10 ), and a spring ( 3 ) between the nozzle body ( 10 ) and the piston ( 2 ). A reducing agent flow channel ( 12 ) extends between a nozzle inlet ( 11 ) and a nozzle orifice ( 14 ), which widens towards a nozzle opening ( 13 ). A piston head ( 21 ) closes or opens the nozzle orifice ( 14 ). The spring ( 3 ) biases the piston ( 2 ) to close the nozzle orifice ( 14 ) with the piston head ( 21 ). A largest diameter (D 13 ) of the nozzle opening ( 13 ) is larger than a largest diameter (D 21 ) of the piston head ( 21 ). An exhaust gas treatment device ( 5 ) includes a tank ( 51 ) for the liquid reducing agent, the nozzle ( 1 ), a reducing agent pump ( 53 ) and a reducing agent conduit ( 52 ). A control ( 54 ) is configured to operate the reducing agent pump ( 53 ) continuously with variable output.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Patent Application No. 10 2016 118 043.2, filed Sep. 23, 2016 in Germany, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to an exhaust gas treatment device for motor vehicles which uses a liquid reducing agent for the treatment of the exhaust gas. More specifically, the present invention relates to a nozzle for a SCR catalytic converter (SCR=selective catalytic reduction) of an exhaust gas treatment system.

BACKGROUND

Flue gas from combustion plants, incineration plants, industrial facilities, as well as exhaust gas from gas turbines and engines often contain nitric oxides NO_(R). Nitric oxides are formed in the thermal utilization of solid, gaseous, and liquid natural and fossil combustibles like coal, gas, oil, and wood. Nitric oxides are particularly present in the exhaust gas from combustion engines for motor vehicles and commercial vehicles. The amount of nitric oxides is particularly high in exhaust gas from diesel powered combustion engines.

Nitric oxides are suspected of irritating or harming the human respiratory system (in particular nitrogen dioxide NO₂). Nitric oxides are further related to the formation of “acid rain” because of the formation of nitric acid (HNO₃) through the reaction (2 NO₂+H₂O→HNO₃+H NO₂) or the absorption of N₂O₅ in aerosol particles followed by the formation of NO₃ ⁻ in the liquid phase. Nitric oxides are further deemed to contribute to the formation of smog and ozone O₃, when exposed to UV radiation.

As a consequence, efforts have been made to reduce the amount of nitric oxides in exhaust gases. For this purpose, it is known to inject an accurately metered nontoxic reducing agent of water and urea CH₄N₂O into the (still hot) exhaust gas stream. This results in the formation of ammonia NH₃ and carbon dioxide CO₂. In a SCR catalytic converter disposed along the exhaust gas stream downstream of the injection, the ammonia reacts with the nitric oxides of the exhaust gas to produce nonhazardous nitrogen N₂ and water H₂O. As reducing agent, urea mixed with water (32.5% aqueous urea solution) can be purchased under the brand name AdBlue (Europe) or Diesel Exhaust Fluid (America), respectively. The reducing agent can be injected mixed with compressed air or directly in liquid form. Using ammonia directly as reducing agent instead of urea is theoretically conceivable but poses problems due to the acid, hazardous and toxic properties of ammonia.

Besides the fact that a reducing agent has to be provided in addition to the fuel, one of the detriments of treating exhaust gas with such a, in particular, liquid reducing agent is that the reducing agent has to be metered in the exact ratio to the nitrogen oxide emission of the combustion engine in order to achieve a high NO_(x) reduction. This requires a thorough mixing of the exhaust gas to be treated and the reducing agent. A respective thorough mixing is promoted by injecting the reducing agent at high pressure (typically 4.5 bar to 8.5 bar) into the exhaust tract passing the exhaust gas to be treated.

Nozzles with integrated active valves are usually used for injecting the reducing agent. These nozzles are prone to failure, because they are subjected to the high temperatures of the exhaust gases and also require electrical energy for their operation. One reason for using nozzles with active valves is that the freezing point of the 32.5% aqueous urea solution is at −11.5° C. The conduit system for delivering the urea solution therefore has to be designed to be drained at temperatures below zero. For draining the conduit system, usually a valve of the nozzle is opened and the direction of flow of a pump delivering the urea solution is reversed such that the urea solution in the conduit system is returned into a tank providing the urea solution. The tank may have a heatable configuration. A further reason for using active valves is that the amount of the injected reducing agent is usually controlled by a corresponding clocking of the nozzle. A respective system is known from US 2014/0182271 A1. A problem with using nozzles having integrated active valves is that these often fail when exposed to the high exhaust gas temperatures.

From the field of steam turbines it is known to use passive nozzles for injecting water into supercritical steam. When used for injecting a reducing agent into a hot exhaust tract, the spray pattern of these nozzles would, however, not sufficiently promote a mixing of the reducing agent and the exhaust gas. As an example for respective nozzles reference is made to WO 2014/055691 A1.

SUMMARY

Embodiments provide an exhaust gas treatment device for motor vehicles and a nozzle configured to be used therein having an increased ruggedness and being thus less sensitive to failure. Further embodiments provide a nozzle for injection of a reducing agent, with the spray pattern of the nozzle promoting a mixing of the reducing agent and the exhaust gas.

Embodiments of a nozzle for an exhaust gas treatment system comprise a nozzle body, a piston moveably disposed inside the nozzle body, and a spring. The nozzle body is configured with a nozzle inlet for a liquid reducing agent and a nozzle orifice for discharging the reducing agent. Further, a flow channel for the reducing agent is provided inside the nozzle body between the nozzle inlet and the nozzle orifice. The flow channel passes the reducing agent from the nozzle inlet to the nozzle orifice. The nozzle orifice is thereby shaped such that it widens from the flow channel towards a nozzle opening. In other words, a diameter of a free cross-sectional area surrounded by the nozzle orifice in a circumferential direction increases from the flow channel towards the nozzle opening. Inside the nozzle body is a moveably disposed piston having a piston head. The piston head is disposed inside the nozzle orifice and configured to selectively close or open the nozzle orifice. The spring is disposed between the nozzle body and the piston and biases the piston in a direction in which the piston head closes the nozzle orifice. A largest diameter of the nozzle orifice is thereby larger than a largest diameter of the piston head.

According to an embodiment, these largest diameters are determined perpendicular to a longitudinal extension of the flow channel or perpendicular to a longitudinal extension of the piston.

The nozzle thus includes an integrated passive valve formed by the piston and the spring that cooperates with the nozzle orifice. Since the nozzle operates passively and has therefore no active components like electric motors or the like, it is very rugged. The excellent ruggedness of the nozzle with respect to high temperatures allows a use of the nozzle in applications, where a flash evaporation of the injected reducing agent is desired. Since the largest diameter of the nozzle orifice is larger than a largest diameter of the piston head, the nozzle orifice extends beyond the piston head at least in an operational state, where the piston head abuts against the nozzle orifice to thereby close it. This results in the nozzle orifice providing a guiding area for the liquid reducing agent exiting the nozzle when opening the nozzle (due to a relative movement between the piston head and the nozzle orifice) and thus controlling the spray pattern.

The nozzle described above opens automatically at a pressure of the supplied reducing agent that can be adjusted with the spring used (or its spring constant), and also closes automatically, when the pressure of the supplied reducing agent falls below this pressure. This prevents a running on of the reducing agent and an infiltration of dirt or the like, when no reducing agent is to be delivered. The output/metering quantity of the nozzle described above depends on the reducing agent's liquid pressure differential in front and behind the nozzle opening. The use of the nozzle further results in that the pressure of the conveyed reducing agent is determined by the nozzle (and, in particular, by the spring used in the nozzle and its spring constant) and is substantially constant. Furthermore, the opening state of the nozzle adapts automatically to a respective output of the reducing agent with the pressure of the reducing agent being substantially constant, thus producing a corresponding spray pattern.

According to an embodiment, the nozzle opening is oriented perpendicular to a longitudinal extension of the flow channel or perpendicular to a longitudinal extension of the piston. According to an embodiment, the spring is disposed inside the nozzle body. According to an alternative embodiment, the spring is disposed outside the nozzle body.

According to an embodiment, the largest diameter of the nozzle opening is larger than a largest diameter of the piston head by at least 5%, or at least 10%. A respective sizing guarantees that the nozzle orifice extends beyond the piston head in all or nearly all positions of the piston head.

According to an embodiment, the extension of the nozzle body around the nozzle orifice is in the longitudinal direction of the flow channel or the longitudinal direction of the piston in each operational state of the piston (i.e. each of the positions of the piston head relative to the nozzle orifice) larger than that of the piston head.

According to an embodiment, the nozzle orifice extends beyond the piston head in an operational state where the piston head abuts against the nozzle orifice to thereby close it by at least one of:

-   -   8.6% or more than 8.6% of the largest diameter (D21) of the         piston head (21);     -   17% or more than 17% of the largest diameter (D21) of the piston         head (21);     -   64% or more than 64% the largest diameter (D21) of the piston         head (21);     -   more than half of the largest diameter (D21) of the piston head         (21).

According to an embodiment, the nozzle orifice forms an opposite angle with the piston head which is in the closing position of the piston at the point of contact of the piston with the nozzle orifice larger than 1° or larger than 2° or larger than 3°. This opposite angle results in an increase in pressure in the reducing agent around the nozzle orifice and promotes a fine spray pattern.

According to an embodiment, an opening angle is formed between the nozzle orifice and a longitudinal extension of the piston at the point of contact of the piston with the nozzle orifice in the closing position of the piston that is smaller than an angle formed between the piston head and the longitudinal extension of the piston at the point of contact of the piston with the nozzle orifice in the closing position of the piston. A respective configuration allows the provision of an opposite angle between the nozzle orifice and the piston head of more than 1° in a simple way.

According to an embodiment, a diameter of a free cross-sectional area surrounded by the nozzle orifice in a circumferential direction increases in the longitudinal direction of the flow channel continuously along a direction on the far side of the flow channel with an increasing gradient. This results in the first derivative of the change of the diameter of the nozzle orifice along the longitudinal direction of the flow channel being also continuous. According to an embodiment, a diameter of the nozzle orifice increases in the longitudinal direction of the piston continuously along the direction facing away from the piston foot with an increasing gradient. This results in the first derivative of the change of the diameter of the nozzle orifice along the longitudinal direction of the piston being also continuous. According to an embodiment, the increasing gradient has a parabolic or hyperbolic progression, with the vertex positioned at the end of the nozzle body at the far side of the flow channel. According to an alternative embodiment, the diameter of the nozzle orifice progresses in the longitudinal direction of the flow channel along a circular path. A respective configuration of the nozzle orifice allows to adjust the spray pattern to different reducing agent outputs.

According to an alternative embodiment, a diameter of a free cross-sectional area surrounded by the nozzle orifice in a circumferential direction increases in the longitudinal direction of the flow channel linearly along a direction on the far side of the flow channel. According to a further alternative embodiment, a diameter of the nozzle orifice increases in the longitudinal direction of the piston linearly along a direction facing away from the piston foot of the piston. Respective nozzle orifices often have the form of a truncated cone's side surface and are particularly easy to manufacture.

According to an embodiment, a diameter of the piston head increases in the longitudinal direction of the piston continuously along a direction facing away from a piston foot of the piston with an increasing gradient. This results in the first derivative of the change of the diameter of the piston head along the longitudinal direction of the piston being also continuous. According to an embodiment, the increasing gradient has a parabolic or hyperbolic progression, with the vertex positioned at the end of the piston head at the far side of the piston foot. According to an alternative embodiment, the diameter of the piston head progresses in the longitudinal direction of the piston along a circular path. A respective configuration of the piston head allows to adjust the spray pattern to different reducing agent outputs.

According to an alternative embodiment, a diameter of the piston head increases in the longitudinal direction of the piston linearly along a direction facing away from the piston foot of the piston.

According to an embodiment, the nozzle opening and a cross section through the piston head perpendicular to the longitudinal direction of the piston each have a circular shape. Respective nozzle openings and piston heads can be manufactured particularly simply and with high precision.

According to an alternative embodiment, the nozzle opening and a cross section through the piston head perpendicular to the longitudinal direction of the piston each have an oval shape.

According to an alternative embodiment, the nozzle opening and a cross section through the piston head perpendicular to the longitudinal direction of the piston each have a geometrically similar polygonal shape.

According to an alternative embodiment, the nozzle opening and a cross section through the piston head perpendicular to the longitudinal direction of the piston each have a geometrically similar asymmetric shape. Using asymmetric cross sections allows to produce very pronounced spray patterns.

The cross sections of the nozzle opening and the piston head are in particular to be regarded as geometrically similar, when they can be transformed into each other by uniform scaling.

According to an embodiment, the transition between a piston foot of the piston and the piston head is continuous in the longitudinal direction of the piston. According to an alternative embodiment, a kink is provided along the longitudinal direction of the piston between the piston foot and the piston head that results in the first derivative of the change of the diameter in the longitudinal direction of the piston not being continuous.

Embodiments of an exhaust gas treatment device for motor vehicles comprise a tank for a liquid reducing agent, a nozzle having an integrated passive valve, a reducing agent conduit for passing the liquid reducing agent from the tank to the nozzle inlet of the nozzle, a reducing agent pump, positioned along the reducing agent conduit between the tank and the nozzle, and a control for controlling the reducing agent pump. The nozzle may thereby have the configuration described above. The control is in this case configured to operate the reducing agent pump and/or the nozzle continuously with variable output.

Accordingly, this exhaust gas treatment device performs the metering of the injected reducing agent not by clocking the nozzle (like when using nozzles with an integrated active valve) or by clocking the reducing agent pump. The reducing agent pump is rather operated continuously and the amount of the output liquid reducing agent controlled instead. As a benefit of this, the non-constant spray patterns of the injected reducing agent at the beginning and the end of each clock cycle are avoided and a constant spray pattern is achieved instead. Using the nozzle having a passive valve ensures that the discharge pressure is maintained at a substantially constant level.

According to an embodiment, a continuous operation of the reducing agent pump refers to the reducing agent pump not being clocked but supplying the nozzle non-intermittently with the reducing agent for at least 10 seconds, and, in particular, for at least 30 seconds, and, further in particular, for at least 100 seconds. According to an embodiment, a continuous operation of the nozzle refers to the nozzle not being clocked but supplying the reducing agent non-intermittently for at least 10 seconds, and, in particular, for at least 30 seconds, and, further in particular, for at least 100 seconds. At such long operating times of the nozzle, the states at the beginning and end of an operation will only be secondary. According to an alternative embodiment, a continuous operation of the reducing agent pump refers to the reducing agent pump supplying the reducing agent to the nozzle during the entire operation of the exhaust gas treatment non-intermittently. According to an alternative embodiment, a continuous operation of the nozzle refers to the nozzle supplying the reducing agent during the entire operation of the exhaust gas treatment non-intermittently.

According to an embodiment, the reducing agent pump is a gear pump. According to an embodiment, the reducing agent pump is an internal gear pump or an external gear pump or a gerotor pump or a screw pump. Respective pumps are very rugged and allow to adjust the volume of the output medium precisely by controlling the rotational speed (number of revolutions) of the reducing agent pump. In the case of substantially incompressible media (as is a liquid reducing agent), the pump volume corresponds to the output. Consequently, no additional measurement device is required for a determination of the output, as long as the rotational speed of the reducing agent pump is determined and the geometry of the reducing agent pump is known.

According to an embodiment, the exhaust gas treatment device further comprises a pressure sensor positioned along the reducing agent conduit between the pump and the nozzle, the pressure sensor being configured to determine the (in particular hydrostatic) pressure of the reducing agent passed in the reducing agent conduit. The use of a respective pressure sensor allows to detect a failure at the nozzle or the reducing agent pump or the reducing agent conduit (or the like), in order to monitor the proper functioning of the exhaust gas treatment device.

According to an embodiment, the exhaust gas treatment device further comprises a heater configured to heat at least one of the tank, the reducing agent conduit, and the nozzle. This allows to prevent a freezing of the reducing agent at low ambient temperatures.

According to an embodiment, the exhaust gas treatment device further comprises a compressed air source configured to blow pressurized air through the reducing agent conduit and the nozzle in order to drain the reducing agent from the reducing agent conduit and the nozzle. The compressed air source may for instance be a compressor or in those cases were a compressor unit is present, a pressure valve. When purging the reducing agent conduit and the nozzle after operation with compressed air, no reducing agent can freeze at low temperatures inside these components.

According to an embodiment, the exhaust gas treatment device further comprises an exhaust gas line for passing exhaust gas to be treated, the nozzle orifice of the nozzle being positioned in the exhaust gas line and, in particular, in the centroid of a cross section through the exhaust gas line. The exhaust gas thus flows around the nozzle orifice. According to an embodiment, the whole nozzle is disposed in the centroid of a cross section through the exhaust gas line. With the nozzle orifice further being oriented in the flow direction of the exhaust gas, a respective configuration enables a particularly uniform distribution of the reducing agent injected. Furthermore, the surrounding exhaust gas then already preheats the reducing agent in the nozzle. The exhaust gas treatment device further comprises a catalytic converter disposed along the flow direction of the exhaust gas passed by the exhaust gas line downstream of the nozzle and being configured for a selective catalytic reduction of the exhaust gas using the reducing agent injected by the nozzle.

The forgoing as well as other advantageous features of the disclosure will be more apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. It is noted that not all possible embodiments necessarily exhibit each and every, or any, of the advantages identified herein. In the following description of exemplary embodiments, reference is made to the enclosed Figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1A is a schematic cross sectional view of a nozzle according to a first embodiment;

FIG. 1B is an enlarged view of a detail of the nozzle of FIG. 1A;

FIG. 2A is a schematic cross sectional view of an orifice region of a nozzle according to a second embodiment in one of different operation states;

FIG. 2B is a schematic cross sectional view of an orifice region of a nozzle according to a second embodiment in another of different operation states;

FIG. 2C is a schematic cross sectional view of an orifice region of a nozzle according to a second embodiment in another of different operation states;

FIG. 3 is a schematic top view and two schematic cross sectional views of an orifice region of a nozzle according to a third embodiment;

FIG. 4 is a schematic top view and two schematic cross sectional views of an orifice region of a nozzle according to a fourth embodiment;

FIG. 5A is a schematic cross sectional view of an orifice region of a nozzle according to a fifth embodiment;

FIG. 5B is a schematic cross sectional view of an orifice region of nozzle according to a sixth embodiment;

FIG. 5C is a schematic cross sectional view of an orifice region of a nozzle according to a seventh embodiment; and

FIG. 6 is a schematic block diagram of an exhaust gas treatment system according to an embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In the exemplary embodiments described below, components that are alike in function and structure are designated as far as possible by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the descriptions of other embodiments and of the summary of the disclosure should be referred to.

Referencing FIGS. 1A and 1B, a nozzle according to a first embodiment is described in the following.

The nozzle 1 comprises a nozzle body 10 made from stainless steel. Overall, the nozzle body 10 has the form of a side surface of a cylinder which one end side is closed and which other end side forms a nozzle orifice 14 with a circular nozzle opening 13. A nozzle inlet 11 in the form of a bore is provided at a side wall of the nozzle body 10 for allowing liquid reducing agent to enter the nozzle 1. A flow channel 12 is formed between the nozzle inlet 11 and the nozzle orifice 14, the flow channel having a constant circular cross section in the embodiment illustrated.

A piston 2 is received inside the nozzle 1, the piston 2 is also made from stainless steel and mounted in the nozzle 1 allowing it to linearly reciprocate along the flow channel 12. At one end, the piston 2 comprises a piston head 21 disposed inside the nozzle orifice 14. At its end opposite the piston head 21, the piston 2 passes through the end side of the nozzle body 10 and is provided with an overall T-shaped piston foot 22. At the transition between the piston head 21 and the long leg of the T-shaped piston foot 22 is a kink.

A coil spring 3 is sandwiched between the piston foot 22 and the nozzle body 10, the coil spring 3 biasing the piston 2 in a direction in which the piston head 21 abuts against a wall of the nozzle orifice 14 to thereby close the nozzle opening 13. This operational state of the nozzle 1 is illustrated in FIGS. 1A and 1B. The coil spring 3 is in this embodiment made from a corrosion resistant nickel-base alloy which can be purchased under the brand name “Inconel” from the Special Metals Corporation based in Huntington, W. Va., USA.

When the pressure of the reducing agent supplied to the nozzle inlet 11 exceeds the bias of the spring 3, the piston 2 is shifted towards the nozzle orifice 14. As a result, the piston head 21 ceases to abut against the wall of the nozzle orifice 14 and unblocks an annular gap. By this annular gap the reducing agent can exit the nozzle 1 through the nozzle opening 13.

As illustrated in FIG. 1B, the nozzle orifice 14 widens linearly from the flow channel 12 towards the nozzle opening 13, thereby forming a first angle with the longitudinal axis L2 of the piston 2. The nozzle orifice 14 thus has the form of a truncated cone's side surface. Also the diameter of the piston head 21 increases linearly around the nozzle orifice 14 towards the nozzle opening 13 thereby forming a second angle with the longitudinal axis L2 of the piston 2. Accordingly, also the piston head 21 has the form of a truncated cone's side surface. The second angle is larger than the first angle so as to form an opposite angle between the piston head 21 and the wall of the nozzle orifice 14. In the illustrated embodiment, the opposite angle is about 8°. The largest diameter D13 of the nozzle opening 13 is further about 8% larger than the largest diameter D21 of the piston head 21. This results in the piston head 21 abutting against a portion of the wall of the nozzle orifice 13 when the nozzle opening 13 is closed, the portion set back relative to the nozzle orifice 13.

A nozzle according to a second embodiment will now be described with reference to FIGS. 2A to 2C. Hereby, in FIGS. 2A to 2C, each of the lower parts shows a cross sectional view of the region of the nozzle orifice 14 while each of the upper parts shows a top view of the nozzle opening 13. Further, FIGS. 2A to 2C show different operational states of the nozzle. Since the nozzle according to the second embodiment is very similar to the nozzle 1 according to the first embodiment described above, in the following, only the differences will be described in more detail, and for the rest it is referred to the description of the first embodiment.

The nozzles according to the first and second embodiment differ in the particular values of the first angle formed between the wall of the nozzle orifice and the longitudinal axis of the piston, the second angle formed between the wall of the piston head and the longitudinal axis of the piston, and the resulting opposite angle. Further, the largest diameter of the nozzle opening 13 is, in the second embodiment, larger by about 47% than the largest diameter of the piston head 21. Finally, the wall of the nozzle body 10 is not tapered to form an acute angle towards the nozzle opening 13, but forms a shoulder around the nozzle opening 13.

FIG. 2A illustrates the nozzle in a closed state, where the nozzle head 21 abuts against the wall of the nozzle orifice 14 to thereby close the nozzle opening 13. This results in the absence of an opening gap 4 between the nozzle orifice 14 and the piston head 21.

FIG. 2B illustrates the nozzle in a slightly opened state, where the piston head 21 no longer abuts against the wall of the nozzle orifice 14. This results in the presence of an opening gap 4 between the nozzle orifice 14 and the piston head 21.

FIG. 2C illustrates the nozzle in a farther opened state than in FIG. 2B, where the piston head 21 is even further spaced from the wall of the nozzle orifice 14. This results in the presence of an opening gap 4 between the nozzle orifice 14 and the piston head 21, which cross sectional area is enlarged with respect to the cross sectional area of the opening gap 4 in FIG. 2B.

A nozzle according to a third embodiment will now be described referencing FIG. 3. The lower part of FIG. 3 hereby shows a first cross section in the region of the nozzle orifice, while the upper part shows a top view of the nozzle opening 13, and the part at the right side shows a second cross section in the region of the nozzle orifice, the directions of the section axes of the first and second cross sections being perpendicular to each other. Since the nozzle according to the third embodiment is very similar to the nozzle 1 according to the first embodiment described above, in the following, only the differences will be described in more detail, and for the rest it is referred to the description of the first embodiment.

The nozzle according to the third embodiment differs from the nozzle according to the first embodiment particularly in that the nozzle opening 13 and a cross section through the piston head 21 in a direction perpendicular to the longitudinal direction of the piston 2 each have an oval shape. Also the nozzle body 10 has an oval shape and an increased wall thickness. Further, in the third embodiment, a diameter of the free cross-sectional area surrounded by the nozzle orifice in a circumferential direction does not increase linearly along the direction on the far side of the flow channel, but increases with a continuously increasing gradient/curvature. The gradient is hereby selected to result in a progressive development of the cross-sectional area of a resulting opening gap, when the piston is shifted linearly.

A nozzle according to a fourth embodiment is now described referencing FIG. 4. The lower part of FIG. 4 hereby shows a first cross section in the region of the nozzle orifice, while the upper part shows a top view of the nozzle opening 13, and the part at the right side shows a second cross section in the region of the nozzle orifice, the directions of the section axes of the first and second cross sections being perpendicular to each other. Since the nozzle according to the fourth embodiment is very similar to the nozzle according to the third embodiment described above, in the following, only the differences will be described in more detail, and for the rest it is referred to the description of the third embodiment.

The nozzle according to the fourth embodiment differs from the nozzle according to the third embodiment only in that the nozzle body 10, the nozzle opening 13 and a cross section through the piston head 21 in a direction perpendicular to the longitudinal direction of the piston each have a geometrically similar asymmetric shape. This allows the spray pattern to be configured more flexibly and to provide, for instance, preferential directions, were a particularly large amount of reducing agent is injected, and non-preferential directions, were a particularly small amount of reducing agent is injected, along the peripheral direction. This allows a specific spray pattern upon an atomizer surface disposed in an exhaust tract, for example.

Nozzles according to a fifth, sixth, and seventh embodiment will now be described referencing FIGS. 5A to 5C. Since these nozzles are very similar to the nozzle 1 according to the first embodiment described above, in the following, only the differences will be described in more detail, and for the rest it is referred to the description of the first embodiment.

As illustrated in FIG. 5A, a piston head which diameter increases linearly in the longitudinal direction of the piston along the direction facing away from a piston foot of the piston, thus resulting in its surface 23 extending linearly along the longitudinal direction of the piston, can be combined with a nozzle orifice 14 which diameter increases in the longitudinal direction of the flow channel continuously along the direction on the far side of the flow channel with an increasing gradient, and thus extends curvilinear. It is to be noted that the transition between the piston foot and the piston head has a kink in this embodiment.

As illustrated in FIG. 5B, a piston head which diameter increases in the longitudinal direction of the piston continuously along the direction facing away from the piston foot with an increasing gradient resulting in its surface 23 being curved along the longitudinal direction of the piston can be combined with a nozzle orifice 14 which diameter increases in the longitudinal direction of the flow channel linearly along the direction on the far side of the flow channel and hence extends linearly. It is to be noted that the transition between the piston foot and the piston head has no kink in this embodiment.

As illustrated in FIG. 5C, a piston head which diameter increases in the longitudinal direction of the piston continuously along the direction facing away from the piston foot with an increasing gradient resulting in its surface 23 being curved along the longitudinal direction of the piston can be combined with a nozzle orifice 14 which diameter increases in the longitudinal direction of the flow channel continuously along the direction on the far side of the flow channel with an increasing gradient and thus also extends curvilinear. It is to be noted that the transition between the piston foot and the piston head has no kink in this embodiment.

An embodiment of an exhaust gas treatment system will now be described referencing the schematic block diagram shown in FIG. 6.

The exhaust gas treatment device 5 comprises a plastic tank 51 for a liquid reducing agent (in the present case an aqueous urea solution). A reducing agent pump 53 and a heater 56 are disposed in the plastic tank 51. The reducing agent pump 53 of the embodiment shown is an internal gear pump and thus a pump which output depends on its speed and which is capable to continuously output a reducing agent. The heater 56 prevents freezing of the reducing agent in the plastic tank 51 and the reducing agent pump 53 or thaws a frozen reducing agent, respectively.

An outlet of the reducing agent pump 53 is in communication with a reducing agent conduit 52 for passing the reducing agent. In the embodiment shown, the reducing agent conduit 52 is a heat resistant plastic hose running into the nozzle inlet 11 of a nozzle 1 having an integrated passive valve as described above with reference to the first embodiment.

In the illustrated embodiment, the nozzle 1 is disposed in the centroid of the cross-sectional area through an exhaust gas line 58 of the exhaust gas treatment device 5 and oriented such that the nozzle orifice is oriented with the nozzle opening in the flow direction of the exhaust gas. The flow direction of the exhaust gas in the exhaust gas line 58 is indicated in FIG. 6 by arrows. This results in the exhaust gas flowing around the nozzle 1.

Downstream of the nozzle 1 the exhaust gas line 58 enters a SCR catalytic converter 59 of the exhaust gas treatment device 5 configured for a selective catalytic reduction of the exhaust gas using the reducing agent injected by the nozzle 1.

Further, a compressed air source in the form of a compressor 57 is provided at the reducing agent conduit 52 adjacent to the tank. The compressor 57 is configured to blow pressurized air through the reducing agent conduit 52 and the nozzle 1 in order to drain the reducing agent from the reducing agent conduit 52 and the nozzle 1, when the reducing agent pump 53 is not in use.

Lastly, a pressure sensor 55 is provided at the reducing agent conduit 52 for determining the hydrostatic pressure of the reducing agent passed in the reducing agent conduit 52.

The reducing agent pump 53, the pressure sensor 55, the heater 56, and the compressor 57 are in communication with a central control 54 of the exhaust gas treatment system 5. The control 54 operates the reducing agent pump 53 continuously during an operation of the exhaust gas treatment device 5 and activates the heater 56 at low temperatures if necessary. Thereby, the control controls the output of the reducing agent pump 53 with the speed of the reducing agent pump 53. The nozzle 1 thereby maintains the discharge pressure at a substantially constant level, since the opening position of the piston of the nozzle 1 adjusts to a respective output. The pressure sensor 55 monitors the proper operation of the system. A pressure indicated by the pressure sensor 55 being too high implies a blockage of the nozzle 1. A pressure indicated by the pressure sensor 55 being too low may suggest a malfunction of the reducing agent pump 53 or a leak in the reducing agent conduit 52.

The control 54 may be in communication with an engine control unit (not shown) and receive from it a request for an amount of reducing agent required for the exhaust gas treatment. Alternatively, the control 54 may also be formed integrally with the engine control unit.

While the disclosure has been described with respect to certain exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the disclosure set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present disclosure as defined in the following claims.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

APPENDIX List of Reference Designations

-   1 nozzle -   10 nozzle body -   11 nozzle inlet -   12 flow channel -   13 nozzle opening -   14 nozzle orifice -   2 piston -   21 piston head -   22 piston foot -   23 surface of the piston head in a peripheral direction -   3 spring -   4 opening gap -   5 exhaust gas treatment device -   51 tank -   52 reducing agent conduit -   53 reducing agent pump -   54 control -   55 pressure sensor -   56 heater -   57 compressed air source -   58 exhaust gas line -   59 catalytic converter -   angle between the nozzle orifice and the longitudinal axis of the     piston -   angle between the piston head and the longitudinal axis of the     piston -   opposite angle between the piston head and the nozzle orifice -   D13 largest diameter of the nozzle orifice -   D21 largest diameter of the piston head -   L2 longitudinal axis of the piston 

What is claimed is:
 1. A nozzle for an exhaust gas treatment system, the nozzle comprising: a nozzle body comprising a nozzle inlet for a liquid reducing agent, a nozzle orifice, a flow channel, for the reducing agent, formed between the nozzle inlet and the nozzle orifice, the nozzle orifice widening from the flow channel towards a nozzle opening; a piston movably disposed inside the nozzle body and having a piston head, the piston head being disposed inside the nozzle orifice and being configured to selectively close or open the nozzle orifice; and a spring sandwiched between the nozzle body and the piston and biasing the piston in a direction in which the piston head closes the nozzle orifice, wherein a largest diameter of the nozzle opening is larger than a largest diameter of the piston head.
 2. The nozzle according to claim 1, wherein the largest diameter of the nozzle opening is larger than a largest diameter of the piston head by at least 5%.
 3. The nozzle according to claim 1, wherein the nozzle orifice extends beyond the piston head at least in an operational state where the piston head abuts against the nozzle orifice to thereby close the nozzle orifice, thus providing a guiding area for the liquid reducing agent exiting the nozzle.
 4. The nozzle according to claim 3, wherein the nozzle orifice extends beyond the piston head in all positions of the piston head.
 5. The nozzle according to claim 3, wherein the nozzle orifice extends beyond the piston head in an operational state where the piston head abuts against the nozzle orifice to thereby close the nozzle orifice by at least one of: 8.6% or more than 8.6% of a largest diameter of the piston head; 17% or more than 17% of a largest diameter of the piston head; 64% or more than 64% the largest diameter of the piston head; more than half of the largest diameter of the piston head.
 6. The nozzle according to claim 1, wherein the nozzle orifice (14) forms an opposite angle with the piston head, the opposite angle being larger than 1° at the point of contact of the piston in a piston closed position.
 7. The nozzle according to claim 1, wherein: a diameter of the nozzle orifice increases in a longitudinal direction of the flow channel or of the piston continuously along a direction facing away from the flow channel or from a piston foot of the piston with an increasing gradient; or a diameter of the nozzle orifice increases in a longitudinal direction of the flow channel of the piston linearly along a direction facing away from the flow channel or from a piston foot of the piston.
 8. The nozzle according to claim 1, wherein: a diameter of the piston head increases in a longitudinal direction of the piston continuously along a direction facing away from a piston foot of the piston with an increasing gradient; or a diameter of the piston head increases in a longitudinal direction of the piston linearly along a direction facing away from a piston foot of the piston.
 9. The nozzle according to claim 1, wherein: the nozzle opening and a cross section through the piston head, perpendicular to a longitudinal direction of the piston, each have a circular shape; or the nozzle opening and a cross section through the piston head, perpendicular to the longitudinal direction of the piston, each have an oval shape; or the nozzle opening and a cross section through the piston head, perpendicular to the longitudinal direction of the piston, each have a geometrically similar polygonal shape; or the nozzle opening and a cross section through the piston head, perpendicular to the longitudinal direction of the piston, each have a similar geometrically asymmetric shape.
 10. The nozzle according to claim 1, wherein the transition between a piston foot of the piston and the piston head is continuous along a longitudinal direction of the piston or has a kink.
 11. An exhaust gas treatment device for motor vehicles, the exhaust gas treatment device comprising: a tank for a liquid reducing agent; a nozzle having an integrated passive valve, the nozzle comprising: a nozzle body comprising a nozzle inlet for a liquid reducing agent, a nozzle orifice, a flow channel, for the reducing agent, formed between the nozzle inlet and the nozzle orifice, the nozzle orifice widening from the flow channel towards a nozzle opening; a piston movably disposed inside the nozzle body and having a piston head, the piston head being disposed inside the nozzle orifice and being configured to selectively close or open the nozzle orifice; and a spring sandwiched between the nozzle body and the piston and biasing the piston in a direction in which the piston head closes the nozzle orifice, wherein a largest diameter of the nozzle opening is larger than a largest diameter of the piston head; a reducing agent conduit for passing the liquid reducing agent from the tank to the nozzle inlet of the nozzle; a reducing agent pump disposed along the reducing agent conduit between the tank and the nozzle; and a control for controlling the reducing agent pump, the control being configured to operate the reducing agent pump continuously with variable output.
 12. The exhaust gas treatment device according to claim 11, wherein the control is further configured to operate the nozzle continuously with variable output.
 13. The exhaust gas treatment device according to claim 11, wherein the reducing agent pump a gear pump comprising one of an internal gear pump or an external gear pump, or a gerotor pump or a screw pump.
 14. The exhaust gas treatment device according to claim 11, further comprising a pressure sensor located along the reducing agent conduit between the reducing agent pump and the nozzle, the pressure sensor being configured to determine a pressure of the reducing agent in the reducing agent conduit.
 15. The exhaust gas treatment device according to claim 11, further comprising a heater configured to heat at least one of the tank, the reducing agent conduit, and the nozzle.
 16. The exhaust gas treatment device according to claim 11, further comprising: a compressed air source configured to blow pressurized air through the reducing agent conduit and through the nozzle in order to drain the reducing agent from the reducing agent conduit and from the nozzle.
 17. The exhaust gas treatment device according to claim 11, further comprising: an exhaust gas line for passing exhaust gas to be treated, the nozzle orifice of the nozzle being positioned centrally in the exhaust gas line; and a catalytic converter disposed along the exhaust gas line downstream of the nozzle and being configured for a selective catalytic reduction of the exhaust gas using the reducing agent injected by the nozzle.
 18. The exhaust gas treatment device according to claim 11, wherein neither the nozzle nor the reducing agent pump are clocked. 